Wilson acquired the governorship, his first elective office, in January 1911, having learned about government mostly from books he wrote about it. (And he wrote “Congressional Government” without ever seeing Congress.)

Eighteen months later he was the Democrats’ presidential nominee.

Christie’s only previous elective office was as county freeholder. But later, as the state’s only U.S. attorney, he became prominent while learning a lot about New Jersey’s gamey political culture by prosecuting some of the participants.

This unsentimental political education prepared him so well for the governorship that today, in his 20th month, he is being importuned to seek the Republican presidential nomination.

He won’t. Here’s why.

He relishes being America’s Caesar - its most powerful governor. He wields a line-item veto, he can revise spending numbers but only down (he blocked $1.3 billion in spending this year), and can exercise a “conditional veto,” rewriting legislation and sending it back to the state legislature for approval.

The governor and the lieutenant governor, who run in tandem, are the only state officials elected statewide. The governor appoints the attorney general, treasurer, comptroller, all judges and all county prosecutors.

Understanding the first rule regarding political power - “use it or lose it” - he has flexed his institutional muscles.

“I don’t want to leave my political capital in my desk drawer to frame when I leave,” he says.

A legislature, he says, “is almost genetically predisposed to inaction.”

To get it to move on his combative agenda for taming public employees unions, he held 30 town meetings in nine months - almost one a week.

The Democratic leader of the state Senate has been an ally. Head of the local ironworkers union, he understands how much private-sector union members resent paying the taxes that fund the perquisites of public-sector unions.

As U.S. attorney, a federal employee, Christie paid 34 percent of his health-care premiums, while state and local employees were paying 1.5 percent of their salaries.

A $60,000 teacher would pay $900 for a $19,000 policy, with taxpayers picking up the other $18,100.

This year, the Democratic-controlled Legislature has agreed to cutting benefits for 750,000 state employees and retirees, increasing current employees’ health care and pension contributions, suspending cost-of-living increases and raising retirement ages.

Projected savings: $120 billion over 30 years.

In the 10 years before Christie became governor, property taxes rose 70 percent, primarily to fund the local salaries, pensions and health care that mayors say account for 75 percent of their costs.

Previous state administrations had raised taxes 115 times in eight years. Christie vetoed a “millionaire’s” tax which the legislature said would raise $500 million, and with which the legislature proposed to fund $3 billion in spending.

Christie says, “I almost wanted to sign it to see that magic happen.”

The previous millionaire’s tax (which expired in 2009 and hit “millionaires” earning $400,000) followed the flight of $70 billion in wealth as “the rich,” including small businesses, left the state.

Taxing the rich is popular, but Christie told New Jersey: “If I let my foot off their throat on the millionaire’s tax, they’re coming after you with the gas tax.”

That is, the 24-cent increase in the tax the Legislature can’t get past him.

Christie was one of the first rocks on which Barack Obama’s overrated political potency crashed.

In 2009, Obama campaigned for Gov. Jon Corzine and against Christie in July, October and the Sunday before Christie won handily.

No one outside of Washington has made more political waves in the last 20 months than Christie, and no one inside Washington has been as successful.

But he has four children, ages 8 to 17, he will not abandon for presidential politics. When he visited a workaholic aide during her difficult labor before her daughter was born, he said, “Put away your BlackBerry, you are in the middle of a miracle.”

As subtle as a linebacker, as direct as an uppercut, Christie, explaining why he will not run, demonstrates why many wish he would.